The voltage-grated sodium channel plays a key role in the generation and propagation of action potentials in excitable cells. Channel activation is associated with a rapid influx of sodium ions down their electrochemical gradient, with a voltage and time dependent inactivation, which provides the rapid and transient depolarization in the membrane potential that is characteristic of the action potential. One of the major strategies to understand how the molecular structure of the channel is related to its function has been based on the purification of channels that retained their native functional properties. Although voltage-gated sodium channels from various sources appear to have basic similarities, subtle differences have been found that might be related to different functional properties. There is little information on the functional significance of these subtypes, and it is this lack of information that has stimulated the present proposal. This project will use a multidisciplinary approach to study purified saxitoxin-sensitive voltage- gated Na a channel subtypes from rat brain, as defined by functional and biochemical differences, in order to further characterize subtype differences and gain information about how these manifested differences might related to different protein structures or post-translational modifications. Sodium channel subtypes will be examined using both biochemical and electrophysiological (planner lipid bilayer and patch clamp) methodology for differences in : 1) subunit composition; 2) glycosylation; 3) neurotoxin binding and effect on single channel properties (i.e. conductance and channel voltage-dependent opening probability); and 4) ion selectivity and permeability (studied in the presence and absence of neurotoxins which remove channel inactivation). Characterization of the biochemical and functional differences as well as similarities between voltage-gated sodium channel subtypes isolated from rat brain will establish the necessary basis for future experiments to probe the structure function relationships in the voltage-gated sodium channel, as well as the regulation of expression and topographical localization of channel subtypes.